The invention relates to an imaging system, in particular for automatic analyzers with a high sample throughput. Such automatic analyzers are frequently termed xe2x80x9creadersxe2x80x9d or xe2x80x9cfluorescence readersxe2x80x9d for microtiter plates. Such xe2x80x9creadersxe2x80x9d are used, for example, in the development of pharmaceutically active materials or in molecular medical diagnoses, and thus in applications in which fluorescence, luminescence, and absorption investigations of large sample numbers and very small sample quantities are required. Consequently a high sample throughput is of great importance in these applications. On the other hand, measurements of reaction kinetics are frequently required, the time constants of which are an obstacle to a high sample throughput.
In these applications, microtiter plates are used, with very small sample containers arranged in an array, in standardized embodiments with, e.g., 96 or a multiple thereof, for example, 384 or 1536, sample containers. As an alternative, so-called substance chips are also in use as sample containers.
In a few applications, the actual task of the measurement is to determine the fraction, or the change with time of the fraction, of a substance which has penetrated from the solution into the interior of a cell or which is bound to the cell surface. The substance concerned is as a rule marked with a fluorescing dye. In this measurement task, it is required to discriminate the fluorescence signal of the dye taken up by, or bound to, the cell from the fluorescence signal of the substance still present in the solution. Since the cells concerned are as a rule situated on the floor of the microtiter plate, a fluorescence reader is consequently required which operates floor-selectively.
A corresponding floor-selective fluorescence reader is offered, for example, by the Molecular Devices Corporation, USA under the name Fluorometric Imaging Plate Reader. In this device, the fluorescence excitation takes place from below through the floor of the microtiter plate at a strongly grazing incidence through a slit mask. The fluorescence light is then detected from that lateral region of the microtiter plate into which the excitation light has penetrated to only a small depth into the sample container, due to the grazing incidence. However, the fluorescence excitation is very ineffective with this device, since only a small fraction of the excited fluorescence is used for the detection. Furthermore, only the fluorescence of a very small lateral region of the sample space floor is used, so that only the cells situated in this small lateral region contribute to the measurement signal.
A line-form imaging system is known form JP 7013101-A in which an array of pentaprisms is arranged between two lens arrays. The lens arrays respectively have a cylindrical lens surface on the side toward the pentaprisms. The pentaprisms then bring about a lateral interchange of the image effected by the whole system in the direction of the axes of the cylindrical lenses.
In the Applicant""s as yet unpublished German patent application 197 48 211, an optical system for a corresponding analytical device is described, in which a lens array with a lens allocated to each sample container is provided on the sample space side. Together with a telescope with a field lens, arranged after the lens array on the detection side, the foci of the individual lenses of the lens array are imaged on a detector array for the production of the desired measurement signal. Signal acquisition here takes place in parallel and simultaneously for all the sample containers, so that a high throughput can be realized with this optical arrangement. Since the measurement signal, for example the detected fluorescence light, originates almost exclusively from the focal volumes of the individual lenses of the lens array, a very depth-selective fluorescence detection is possible with this optical arrangement. Here also, the lateral cross section, that is, perpendicular to the optical axes of the lenses of the lens array, of the detection volume is of course very small. Furthermore, the detection of the fluorescence or of another measurement signal from the region of the floor of the sample container requires in practice a depth scan, and thus several measurements with different distances between the microtiter plate and the optical arrangement in the direction of the optical axis, since the individual floors of the sample containers of the microtiter plate have different heights, due to production conditions. The time required for a depth scan is however contrary to the aim of a high sample throughput.
The present invention has as its object to provide an imaging system which makes possible measurements in parallel in plural sample containers. The measurement signals acquired in parallel are to have an identical sensitivity in all the sample containers, even when the floor height of the sample containers is different, and to make possible a discrimination of the measurement signals originating from the region near the floor, and a high sample throughput.
This object is attained according to the invention by an imaging system with the features of claim 1. Advantageous developments of the invention will become apparent from the features of the dependent claims.
The imaging system according to the invention consequently has an array of cylindrical lenses. A prism array is arranged before this cylindrical lens array on the sample side, the prism array being oriented relative to the cylindrical lens array such that the prismatic effect of the prisms is in the direction of the cylinder axes of the cylindrical lenses. The cylindrical lens array and the prism array can be constituted here as two separate components or as a single component. In the latter case, the combined array has, on a common support, a constitution as a prism array on the sample side and the cylindrical lenses on the side remote from the sample. Due to the cylindrical lenses, a substantially cylindrical detection volume results in each of the sample containers. Due to the prisms arranged on the sample side in front of the cylindrical lenses, the cylinder axes of the focal volume receive an inclination relative to the cylinder axes of the cylindrical lenses. If the cylindrical lens array is arranged substantially parallel to the microtiter plate, cylindrical detection volumes thereby result which are inclined to the floors of the sample containers. Since the cross sectional surfaces through the detection volumes are identical for parallel sections through these detection volumes, the detection of the measurement signal from different depths of the sample volume takes place with identical sensitivity. Consequently even different floor heights in the different sample containers do not give rise to different measurement sensitivities.
It should be mentioned at this point that an imaging system for the projection of color LCD displays as the object to be imaged is already known from U.S. Pat. No. 5,602,679, in which a lens array with a superposed prismatic effect is used. Cylindrical lenses are also stated there as a possible lens form of the lens array. Although no specific data are given, it is to be concluded therefrom that the prism action of the prisms has to be oriented perpendicular to the cylinder axes of the cylindrical lenses, so that the desired superposition of the color pixels is attained. Apart from this, the statement of objects given there completely departs from the statement of object of the present invention.
The imaging system according to the invention is preferably used, similarly to that of the German Patent Application 197 48 211 mentioned hereinabove, together with a telescopic imaging system, the long-focus lens of the telescopic imaging system being oriented in the direction toward the cylindrical lens array, and overlapping with its diameter plural, preferably all the, cylindrical lenses. A detector array is then preferably arranged after the imaging system or the telescopic imaging system, and with it the measurement light for the different parallel channels of the imaging system is detected in parallel. The detector array is then furthermore preferably arranged behind the exit-side focal plane of the telescope lens remote from the cylindrical lens array, the said focal plane being remote from the long-focus telescope lens and the cylindrical lens array. With such an optical arrangement, different lateral displacements of the intensity distribution of the measurement light on the detector array result from different heights of the floor of the microtiter plate. Since as a rule the maximum measurement signal, for example, the maximum fluorescence intensity, originates from the transition region from the sample space floor into the solution, the measurement signal resulting from this region can thereby be easily discriminated from the remaining measurement signal in that only the regions of the detector array with maximum signal strengths are made use of for further evaluation. In this manner, the measurement signal originating from the floor region can quickly and easily be discriminated from the measurement originating from the solution.
The imaging system according to the invention can in principle be combined with the telescopic imaging system and the detector array into a single constructional unit. However, a modular construction is particularly advantageous, in which the cylindrical lens array and the prism array form their own constructional unit. This constructional unit can then be easily exchanged for the lens array from the above cited patent application 197 48 211, so that the functionality of the reader described there can be correspondingly enlarged. Alternatively, a reader constructed according to the present invention can easily be changed to a reader according to DE 197 48 211 by exchange of the constructional unit with the lens array on the sample side, and by insertion or exchange of a spacing ring for a constructional unit with a field lens between the two telescope lenses.
In the present invention, the apertures of the cylindrical lenses are imaged on the detector array by the telescopic imaging system.
For the excitation of fluorescence or luminescence, a vertical illuminator is to be provided, light from which is reflected into the measurement beam path, preferably between the detector array and the short-focus telescope lens.
In a completely automatic analyzer with an optical imaging system according to the invention, an evaluation computer for the evaluation of the light signals detected with the detector array is to be provided. This evaluation computer can carry out an integration of the light signals belonging to each sample container, in the direction perpendicular to the cylinder axes of the cylindrical lens array, and then, by means of software, determine solely the maximum value of the integrated light intensity or the other characteristic signal change in the direction of the cylinder axes of the cylindrical lenses, in order to thereby discriminate the measurement signal originating from the floor region of the sample volumes.